JP2018168226A - Paste-like silver powder composition, method for producing joined body, and method for producing silver film - Google Patents

Abstract

The present invention provides a paste-like silver powder composition which is excellent in coatability and capable of forming a silver film (bonding layer) having high heat dissipation and bonding properties by heating at a relatively low temperature. The silver powder contains a silver powder, a polymer dispersant having a nitrogen atom or a phosphorus atom in the molecule, and at least one solvent selected from the group consisting of diols and carbitol acetates. The detected amount of each of C3H3O3- ions and C6H6O8- ions measured by time-type secondary ion mass spectrometry is 0.2 times or more that of Ag+ ions. 0 times or less, the amount of detection of C6H6O8- ions is in the range of 0.005 times or more and 0.02 times or less, and the polymer dispersant has a peak top molecular weight of 1500 or more and 15000 or less as measured by gel filtration chromatography. and the content of the polymer dispersant is in the range of 1% by mass or more and 5% by mass or less. [Selection drawing] Fig. 1

Description

  The present invention relates to a paste-like silver powder composition, a method for producing a joined body using the paste-like silver powder composition, and a method for producing a silver film.

  It is known that a fine metal powder composed of metal nanoparticles having a nano particle size can be sintered at a temperature lower than the original melting point of the metal. In particular, since silver powder has high conductivity and heat dissipation, a paste-like silver powder composition in which fine silver powder is dispersed in a solvent is a bonding material for bonding a circuit board and an electronic component such as a semiconductor chip or LED element. And as a raw material for electrodes of solar cell elements.

  For example, Patent Document 1 discloses that silver fine particles having an average primary particle diameter of 1 to 50 nm coated with an organic compound having 8 or less carbon atoms such as hexanoic acid, and an average primary particle diameter of 0.1 .mu.m coated with an organic compound such as oleic acid. A paste-like silver powder composition containing 5 to 4 μm silver particles, a solvent composed of a primary alcohol solvent and a terpene alcohol solvent, and a dispersant composed of a phosphate ester dispersant is disclosed.

Japanese Patent Laying-Open No. 2015-225842

  With the recent miniaturization and higher functionality of electrical equipment, higher integration of semiconductor elements has been promoted, and the amount of heat generated in the semiconductor elements tends to increase. For this reason, in the paste-like silver powder composition, it is desired that a dense silver film (silver powder sintered body) with few pores can be formed in a fine pattern by heating at as low a temperature as possible. By forming a dense silver film, the substrate circuit and the semiconductor element can be bonded with high bonding strength, and the heat conductivity is increased, so that the heat generated in the semiconductor element is easily released to the outside. Has the advantage that damage due to thermal expansion and contraction hardly occurs.

  Conventionally, in order to be able to form a dense silver film, it has been studied to increase the concentration of silver powder in a paste-like silver powder composition. However, when the concentration of the silver powder in the paste-like silver powder composition is increased, the viscosity increases, the applicability decreases, and it may be difficult to form a silver film with a fine pattern. In addition, as described in Patent Document 1, in order to reduce the viscosity of the pasty silver powder composition, it has been studied to add a dispersant. However, the addition of a dispersant hinders the sintering of silver powder during heating, and the density of the resulting silver film is rather lowered, resulting in a decrease in heat dissipation and bondability.

  This invention is made | formed in view of the situation mentioned above, Comprising: It is excellent in applicability | paintability and can form the silver film (silver powder sintered compact) with high heat dissipation and joining property by the heating at comparatively low temperature. The object is to provide a paste-like silver powder composition. The present invention also provides a method for manufacturing a bonded body capable of manufacturing a bonded body having high thermal conductivity and high bonding strength by heating at a relatively low temperature, and a silver film having high thermal conductivity by heating at a relatively low temperature. Another object of the present invention is to provide a method for producing a silver film.

In order to solve the above problems, the paste-like silver powder composition of the present invention is selected from the group consisting of silver powder, a polymer dispersant having a nitrogen atom or phosphorus atom in the molecule, diols and carbitol acetates. and at least one solvent is, the silver powder is measured by time-of-flight secondary ion mass spectrometry, C ₃ H ₃ O ₃ ^- ions and C ₆ H ₆ O ₈ ^- each detected amount of ions However, the detected amount of C ₃ H ₃ O ₃ ⁻ ions is 0.2 to 1.0 times the detected amount of Ag ⁺ ions, and the detected amount of C ₆ H ₆ O ₈ ⁻ ions is 0.1. 005 times or more and 0.02 times or less, and the polymer dispersant has a peak top molecular weight measured by gel filtration chromatography in the range of 1500 to 15000, and contains the polymer dispersant. The content is in the range of 1% by mass to 5% by mass.

In the paste-like silver powder composition having this configuration, the silver powder is coated with an organic compound detected as C ₃ H ₃ O ₃ ⁻ ions and C ₆ H ₆ O ₈ ⁻ ions by time-of-flight secondary ion mass spectrometry. Therefore, aggregation of silver particles is suppressed and the applicability of the paste-like silver powder composition is improved. The detected amounts of C ₃ H ₃ O ₃ ⁻ ions and C ₆ H ₆ O ₈ ⁻ ions measured by this time-of-flight secondary ion mass spectrometry are compared to the detected amount of Ag ⁺ ions. The detected amount of C ₃ H ₃ O ₃ ⁻ ions is in the range of 0.2 to 1.0 times, and the detected amount of C ₆ H ₆ O ₈ ⁻ ions is in the range of 0.005 to 0.02 times. Yes, since the amount of organic compound covering the particle surface is small, the organic compound disappears and the surface of the silver particle is exposed by heating at a relatively low temperature, so the silver particles are sintered at a relatively low temperature. It becomes possible to make it.

  Further, in the paste-like silver powder composition having the above-described configuration, the polymer dispersant having a nitrogen atom or a phosphorus atom in the molecule adheres to the surface of the silver particle, whereby aggregation of the silver particles is suppressed, and the paste-like silver powder composition The applicability of the silver powder composition is improved. Furthermore, since the polymer dispersant has a peak top molecular weight of 1500 or more as measured by gel filtration chromatography, aggregation of silver particles is reliably suppressed. In addition, since the polymer dispersant has a peak top molecular weight of 15000 or less, it can be easily detached from the surface of the silver particles during heating, and the silver particles can be sintered at a relatively low temperature.

  Thus, in the paste-like silver powder composition having the above-described configuration, aggregation of silver particles is suppressed by combining the organic compound covering the surface of the silver particles and the polymer dispersant. For this reason, even if content of a polymer dispersing agent is the range of 1 mass% or more and 5 mass% or less and a comparatively small quantity, the applicability | paintability of a paste-form silver powder composition can be improved. And since content of a polymer dispersing agent is comparatively small with 5 mass% or less, it becomes possible to sinter silver particle by the heating at comparatively low temperature. Therefore, a silver film having high heat dissipation and high bondability can be obtained by heating at a relatively low temperature.

  Furthermore, since the paste-like silver powder composition having the above-described structure contains at least one solvent selected from the group consisting of diols and carbitol acetates, the coatability is further improved.

Here, in the paste-like silver powder composition of the present invention, the polymer dispersant is preferably a polymer dispersant having an amino group or a phosphate group. That is, the nitrogen atom in the molecule is preferably present as an amino group and the phosphorus atom is present as a phosphate group.
In this case, the polymer dispersant can be reliably attached to the surface of the silver particles, and thereby the applicability of the pasty silver powder composition can be further improved.

In the pasty silver powder composition of the present invention, the solvent is preferably ethylene glycol, 2-ethyl-1,3-hexanediol, or butyl carbitol acetate.
In this case, the applicability of the pasty silver powder composition is reliably improved.

  The method for manufacturing a joined body according to the present invention is a method for producing a joined body in which a first member and a second member are joined together via a joining layer, the first member and the second member, A laminating step for forming a laminated body laminated via the pasty silver powder composition of the present invention, and heating the laminated body to dry and sinter the pasty silver powder composition to form a bonding layer. And a sintering step to be generated.

  According to the method for manufacturing a bonded body having this configuration, since the paste-like silver powder composition described above is used as a bonding material for generating a bonding layer, a bonded body having high thermal conductivity and high bonding strength is manufactured by heating at a relatively low temperature. can do.

  The method for producing a silver film of the present invention comprises a step of applying a paste silver powder composition of the present invention to a substrate, and heating the substrate coated with the paste silver powder composition to form the paste And a sintering step of forming a silver film by drying and sintering the silver powder composition.

  According to the method for producing a silver film having this configuration, since the paste-like silver powder composition described above is used as a material for the silver film, a silver film having high thermal conductivity can be produced by heating at a relatively low temperature.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the paste-form silver powder composition which is excellent in applicability | paintability and can form a silver film (silver powder sintered compact) with high heat dissipation and joining property by the heating at comparatively low temperature. It becomes. Further, according to the present invention, a method for producing a joined body capable of producing a joined body having high thermal conductivity and high bonding strength by heating at a relatively low temperature, and silver having high thermal conductivity by heating at a relatively low temperature. It is possible to provide a method for producing a silver film that can produce a film.

It is sectional drawing of the conjugate | zygote manufactured using the manufacturing method of the conjugate | zygote of this embodiment.

  Hereinafter, a paste-like silver powder composition, a method for producing a joined body, and a method for producing a silver film, which are embodiments to which the present invention is applied, will be described in detail. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent.

<Paste silver powder composition>
The pasty silver powder composition of this embodiment contains silver powder, a polymer dispersant, and a solvent. Hereinafter, each of these components will be described.

(Silver powder)
The silver powder used in the present embodiment is composed of pure silver and a silver alloy containing silver as a main component (silver content is 99% by mass or more). The average particle diameter of the silver powder is a nano size of 100 nm or more and 150 nm or less. By using silver powder containing silver in high purity and having an average particle size of nano-size, by heating at a temperature lower than the original melting point of silver, for example, 130 ° C. or higher, preferably 150 ° C. or higher. It becomes possible to sinter silver powder.

In the silver powder used in the present embodiment, each of the detected amounts of C ₃ H ₃ O ₃ ⁻ ions and C ₆ H ₆ O ₈ ⁻ ions is Ag ^{+ in} time-of-flight secondary ion mass spectrometry (TOF-SIMS). The detected amount of C ₃ H ₃ O ₃ ⁻ ions is 0.2 to 1.0 times the detected amount of ions, and the detected amount of C ₆ H ₆ O ₈ ⁻ ions is 0.005 to 0 times 0. .02 times or less.

C ₃ H ₃ O ₃ ⁻ ions and C ₆ H ₆ O ₈ ⁻ ions detected in time-of-flight secondary ion mass spectrometry are derived from an organic compound (protective agent) covering the surface of the silver particles.
C ₃ H ₃ O ₃ ^- ions and C ₆ H ₆ O ₈ ^- the detection of ions is too small, i.e. the surface activity of the amount is small becomes excessively when silver particles of the organic compound coating the silver particle surface Thus, the silver particles are likely to aggregate, the viscosity of the pasty silver powder composition is increased, and the applicability may be reduced. On the other hand, C ₃ H ₃ O ₃ ^- ions and C ₆ H ₆ O ₈ ^- the detection of the ion is too high, i.e. the amount of the organic compound coating the silver particle surface is too large, sinterability It may be necessary to increase the heating temperature for sintering the silver powder.

For the above reasons, in this embodiment, the detected amount of C ₃ H ₃ O ₃ ⁻ ions is 0.2 to 1.0 times the detected amount of Ag ⁺ ions, and C ₆ H ₆ O _8. ^- detection of ions is in the range of less than 0.02 times 0.005 times. In order to surely improve the storage stability of silver powder and to surely reduce the sintering temperature, the detected amount of C ₃ H ₃ O ₃ ⁻ ions relative to the detected amount of Ag ⁺ ions is 0.3 times or more 0 It is preferable that it is 5 times or less. Moreover, the organic compound adhering to the surface of the silver particles is preferable because it has a low molecular weight because it is easily lost by heating. Therefore, it is preferable that the detected amount of C ₃ H ₃ O ₃ ⁻ ions is larger than the detected amount of C ₆ H ₆ O ₈ ⁻ ions. C ₃ H ₃ O ₃ ^- detection of _ions, C ₆ H _{6 O 8} ^- is preferably in the range of 30 times 50 times or less with respect to the detection of ions.

  Although it does not specifically limit as a shape of the silver particle of silver powder, Specifically, spherical shape, rod shape, scale shape, etc. are mentioned, for example.

  Content of the silver powder in a paste-form silver powder composition exists in the range of 75 mass% or more and 95 mass% or less, for example. If the silver powder content is too low, it may be difficult to produce a high-density silver film. On the other hand, if the content of silver powder becomes too large, the viscosity of the paste-like silver powder composition becomes high and the applicability may be lowered.

  The above silver powder is prepared by, for example, simultaneously dropping an aqueous silver salt solution and an aqueous carboxylic acid solution in which a carboxylic acid or a carboxylic acid salt is dissolved into water to produce silver carboxylate particles to prepare a silver carboxylate slurry. A second step of preparing a silver powder slurry by dropping a reducing agent aqueous solution into the silver carboxylate slurry and preparing a silver powder slurry by heat-treating the resulting mixed slurry to reduce silver carboxylate particles to form silver particles; And a third step of recovering silver powder from the silver powder slurry.

  In the first step, since the silver salt aqueous solution and the carboxylic acid aqueous solution are simultaneously dropped into water, the silver salt concentration and the carboxylate concentration in the water are lowered. For this reason, the reaction rate between the silver salt concentration and the carboxylate is decreased, and fine silver carboxylate particles having a nano-sized particle size are generated.

  The ratio of the amount of the silver salt aqueous solution and the carboxylic acid aqueous solution simultaneously dropped into water is the equivalent ratio of silver and carboxylic acid [= (valence of silver ions: 1 valence × number of moles) / (valence of carboxylic acid × number of moles). ]] Is preferably in the range of 1.1 to 2.0. In this case, as the amount of free carboxylic acid increases in water as the dropping proceeds, the time from dropping the aqueous silver salt solution to the formation of silver carboxylate particles is shortened. It becomes easy to produce silver oxide particles.

  Here, when preparing the silver carboxylate slurry, it is preferable to maintain the temperature of each solution of the silver salt aqueous solution, the carboxylic acid aqueous solution, and water (silver carboxylate slurry) at a predetermined temperature in the range of 20 to 50 ° C. . By maintaining the temperature of each liquid at a predetermined temperature of 20 ° C. or higher, silver carboxylate particles are easily generated, and the particle size of the silver carboxylate particles can be increased. Further, by maintaining the temperature of each liquid at a predetermined temperature of 50 ° C. or lower, it is possible to prevent silver carboxylate particles from growing excessively and becoming coarse particles.

  Moreover, it is preferable that water is stirred while the silver salt aqueous solution and the carboxylic acid aqueous solution are simultaneously dropped into water.

  As the silver salt aqueous solution, an aqueous solution of one or more silver salt compounds selected from the group consisting of silver nitrate, silver chlorate and silver phosphate can be used.

  As the carboxylic acid aqueous solution, an aqueous solution of one or more carboxylic acids or salts thereof selected from the group consisting of glycolic acid, citric acid, malic acid, maleic acid, malonic acid, fumaric acid, succinic acid and tartaric acid is used. Can be used. Since these carboxylic acids form a stable chelate with silver, they are easily precipitated as silver carboxylate particles. The carboxylate is preferably an ammonium salt or alkali metal salt of these carboxylic acids.

  As water, ion-exchanged water or distilled water can be used. It is particularly preferable to use ion-exchanged water because it does not contain ions that may adversely affect the formation of silver carboxylate particles and the production cost is lower than that of distilled water.

In the second step, it is preferable to perform a heat treatment in which the mixed slurry obtained by dropping the aqueous reducing agent solution into the silver carboxylate slurry is held at a temperature in the range of 92 ° C to 95 ° C. By setting the holding temperature of the mixed slurry to 92 ° C. or higher, silver carboxylate is easily reduced, and silver particles can be generated quickly. Moreover, by setting the holding temperature of the mixed slurry to 95 ° C. or lower, the carboxylic acid can be attached as C ₃ H ₃ O ₃ ⁻ ions or C ₆ H ₆ O ₈ ⁻ ions to the surface of the generated silver particles. Therefore, silver particles can be prevented from becoming coarse particles.

  The time for holding the mixed slurry at the above temperature is preferably in the range of 0.25 to 0.5 hours. By setting the holding time to 0.25 hours or longer, silver carboxylate can be reliably reduced, and silver particles can be generated stably. Moreover, it can prevent that the produced | generated silver particle turns into a coarse particle by making holding time into 0.5 hour or less.

  As one method for bringing the mixed slurry to the above-mentioned temperature, a method of preparing the mixed slurry at a temperature of less than 92 ° C. and then heating can be mentioned. In this method, it is preferable to set the temperature rising rate of the mixed slurry in the range of 15 to 20 ° C./hour. By increasing the rate of temperature rise to 15 ° C./hour or more, silver particles can be prevented from becoming coarse particles. By setting it to 20 ° C./hour or less, the liquid temperature inside the mixed slurry is less likely to be uneven.

Another method for adjusting the mixed slurry to the above temperature is to heat the silver carboxylate slurry and the reducing agent aqueous solution and maintain the liquid temperature within the range of 92 to 95 ° C. An example is a method of dropping a reducing agent aqueous solution into the slurry. In this method, the liquid temperature inside the mixed slurry is less likely to be uneven.
be able to.

  As the reducing agent aqueous solution, an aqueous solution of one or more compounds selected from the group consisting of hydrazine, ascorbic acid, oxalic acid, formic acid, and salts thereof can be used.

  The prepared silver powder slurry is preferably cooled quickly in order to prevent the silver particles from becoming coarse particles. The cooling of the silver powder slurry is preferably performed at a temperature lowering rate at which the time for lowering the temperature to 30 ° C. is 15 minutes or less.

  In the third step, silver powder is recovered from the silver powder slurry. As a method for collecting the silver powder, a method of drying the silver powder slurry can be used. Before drying the silver powder slurry, it is preferable to remove the liquid layer in the silver powder slurry using a centrifuge, and to dehydrate and desalt the silver powder slurry.

  Although it does not specifically limit as a drying method of a silver powder slurry, Specifically, a freeze-drying method, a reduced pressure drying method, a heat drying method etc. are mentioned, for example. The freeze-drying method is a method in which a silver powder slurry is put in a sealed container and frozen, the inside of the sealed container is depressurized with a vacuum pump to lower the boiling point of the material to be dried, and the moisture of the material to be dried is sublimated at a low temperature and dried. is there. The reduced-pressure drying method is a method of drying an object to be dried by reducing the pressure. The heat drying method is a method of drying an object to be dried by heating.

(Polymer dispersant)
The polymer dispersant used in this embodiment has a nitrogen atom or a phosphorus atom in the molecule. The molecular weight of the polymer dispersant is in the range of 1500 to 15000 as the peak top molecular weight measured by gel filtration chromatography. In this embodiment, the nitrogen atom in the molecule exists as an amino group, and the phosphorus atom exists as a phosphate group. In this case, it is considered that the polymer dispersant is attached to the organic substance covering the surface of the silver particles via an amino group or a phosphate group. When the polymer dispersant adheres to the surface of the silver particles, aggregation of the silver particles is suppressed, and the applicability of the pasty silver powder composition is improved. In addition, amino groups or phosphate groups are easily detached from the surface of silver particles by heating at a relatively low temperature. For this reason, silver particles can be sintered by heating at a relatively low temperature.

  If the peak top molecular weight of the polymer dispersant becomes too small, the effect of suppressing the aggregation of silver particles becomes weak, the silver particles aggregate, the viscosity of the paste-like silver powder composition increases, and the paste-like silver powder composition The applicability of the coating may be reduced. On the other hand, if the peak top molecular weight of the polymer dispersant is too large, the polymer dispersant is difficult to be detached from the surface of the silver particles during heating, and the heat dissipation and bonding properties of the resulting silver film may be reduced. For this reason, in this embodiment, the peak top molecular weight of the polymer dispersant is set in the range of 1500 to 15000.

  The position of the amino group or phosphate group of the polymer dispersant is not particularly limited, and may be in the main chain or in the side chain. Moreover, you may exist in a principal chain and a side chain, respectively. The polymer dispersant may have an amino group and a phosphate group.

  The content of the polymer dispersant is in the range of 1% by mass to 5% by mass. If the content of the polymer dispersant is too small, the effect of suppressing the aggregation of silver particles becomes weak, and the applicability of the pasty silver powder composition may be reduced. On the other hand, if the content of the polymer dispersant is excessively large, the amount of the polymer dispersant remaining on the surface of the silver particles during heating increases, and the heat dissipation and bonding properties of the resulting silver film may be reduced. .

(solvent)
The pasty silver powder composition of the present embodiment contains at least one selected from the group consisting of diols and carbitol acetates as a solvent.
The diol is preferably a chain hydrocarbon diol. The chain hydrocarbon diol may have a branch. Examples of diols include ethylene glycol, diethylene glycol, polyethylene glycol, and 2-ethyl-1,3-hexanediol. Examples of carbitol acetates include butyl carbitol acetate and ethyl carbitol acetate. These solvent may be used individually by 1 type, and may be used in combination of 2 or more type. The solvent is preferably ethylene glycol, 2-ethyl-1,3-hexanediol or butyl carbitol acetate.

  The content of the solvent is in the range of 1% by mass to 20% by mass. When the content of the solvent is too low, the viscosity of the pasty silver powder composition is increased, and the applicability may be lowered. On the other hand, when the content of the solvent is excessively large, the content of the silver powder is relatively decreased, which may make it difficult to form a dense silver film.

  The pasty silver powder composition preferably has a viscosity of 50 Pa · s or less, and more preferably 15 Pa · s or more and 40 Pa · s or less. The viscosity of the pasty silver powder composition can be measured using a rheometer.

(Method for producing paste-like silver powder composition)
The paste-like silver powder composition of the present embodiment can be produced by kneading the above-described silver powder, polymer dispersant, and solvent at a mixing ratio that results in the above contents. There is no restriction | limiting in particular as a kneading | mixing method, It can carry out using the various kneading machines currently used for manufacture of the conventional paste-form silver powder composition.

In the paste-like silver powder composition of the present embodiment configured as described above, silver powder is obtained by C ₃ H ₃ O ₃ ⁻ ions and C ₆ H ₆ O ₈ ⁻ ions by time-of-flight secondary ion mass spectrometry. Since it coat | covers with the organic compound detected as, aggregation of silver particles is suppressed and the applicability | paintability of a paste-form silver powder composition improves. The detected amounts of C ₃ H ₃ O ₃ ⁻ ions and C ₆ H ₆ O ₈ ⁻ ions measured by this time-of-flight secondary ion mass spectrometry are compared to the detected amount of Ag ⁺ ions. The detected amount of C ₃ H ₃ O ₃ ⁻ ions is in the range of 0.2 to 1.0 times, and the detected amount of C ₆ H ₆ O ₈ ⁻ ions is in the range of 0.005 to 0.02 times. Yes, since the amount of organic compound covering the particle surface is small, the organic compound disappears and the surface of the silver particle is exposed by heating at a relatively low temperature, so the silver particles are sintered at a relatively low temperature. It becomes possible to make it.

  Further, in the paste-like silver powder composition of the present embodiment, the polymer dispersant having a nitrogen atom or a phosphorus atom in the molecule adheres to the surface of the silver particles, whereby aggregation of the silver particles is suppressed, and the paste-like silver powder composition The applicability of the silver powder composition is improved. Furthermore, since the polymer dispersant has a peak top molecular weight of 1500 or more as measured by gel filtration chromatography, aggregation of silver particles is reliably suppressed. In addition, since the polymer dispersant has a peak top molecular weight of 15000 or less, it can be easily detached from the surface of the silver particles during heating, and the silver particles can be sintered at a relatively low temperature.

  Thus, in the paste-like silver powder composition of the present embodiment, aggregation of silver particles is suppressed by combining the organic compound covering the surface of the silver particles and the polymer dispersant. For this reason, even if content of a polymer dispersing agent is the range of 1 mass% or more and 5 mass% or less and a comparatively small quantity, the applicability | paintability of a paste-form silver powder composition can be improved. And since content of a polymer dispersing agent is comparatively small with 5 mass% or less, it becomes possible to sinter silver particle by the heating at comparatively low temperature. Therefore, a silver film having high heat dissipation and high bondability can be obtained by heating at a relatively low temperature.

  Furthermore, since the paste-like silver powder composition having the configuration of the present embodiment contains at least one solvent selected from the group consisting of diols and carbitol acetates, the coatability is further improved.

  In the paste-like silver powder composition of the present embodiment, the polymer dispersant is preferably present as a nitrogen atom in the molecule as an amino group and a phosphorus atom as a phosphate group. It can be made to adhere more reliably to the surface of the silver particles, whereby the applicability of the pasty silver powder composition can be further improved.

  The paste-like silver powder composition of this embodiment may further contain additives such as an antioxidant, a viscosity modifier, and a surfactant depending on the application. These additives may be used individually by 1 type, and may be used in combination of 2 or more type.

<Method for producing joined body>
Next, the manufacturing method of the joined body of this embodiment is demonstrated with reference to FIG.
FIG. 1 is a cross-sectional view of a bonded body manufactured using the bonded body manufacturing method of the present embodiment. In FIG. 1, the bonded body 11 is schematically configured to include a substrate 12, a first metal layer 13, a bonding layer 14, a second metal layer 15, and an object to be bonded 16.

  In this embodiment, as an example, the bonded body 11 in which the substrate 12 (first member) and the workpiece 16 (second member) are bonded using the above-described paste-like silver powder composition will be described. It does not specifically limit as what joins using a silver powder composition.

  Although it does not specifically limit as the board | substrate 12, Specifically, the insulating board etc. which the aluminum plate and the aluminum plate were joined are mentioned, for example.

  The first metal layer 13 is laminated adjacent to the substrate 12. The substrate 12 and the bonding layer 14 are bonded via the first metal layer 13. Specifically, as the material of the first metal layer 13, for example, one or more metals selected from the group consisting of gold, silver, copper, and the like can be used.

The bonding layer 14 is laminated adjacently between the first metal layer 13 and the second metal layer 15.
The bonding layer 14 is in contact with the first metal layer 13 to form an interface 17. The bonding layer 14 is in contact with the second metal layer 15 to form an interface 18. For the bonding layer 14, the paste-like silver powder composition described above is applied onto the first metal layer 13, and the object 16 is placed so that the applied surface and the second metal layer 15 face each other, followed by heat treatment. It consists of the silver film (silver powder sintered compact) formed by.

  The thickness of the bonding layer 14 is not particularly limited as long as the thickness can bond the substrate 12 and the workpiece 16 to each other. Specifically, for example, 1-100 micrometers may be sufficient.

The second metal layer 15 is a bonding layer 14 and is laminated adjacent to the opposite side of the first metal layer 13. The bonding layer 14 and the workpiece 16 are bonded via the second metal layer 15.
As the material of the second metal layer 15, the same material as that used for the first metal layer 13 can be used.

  The workpiece 16 is the second metal layer 15 and is laminated adjacent to the opposite side of the bonding layer 14. Although it does not specifically limit as the to-be-joined object 16, Specifically, a silicon | silicone (Si) chip | tip, a silicon carbide (SiC) etc. are mentioned, for example. Moreover, in the manufacturing method of the joined body 11 of this embodiment, since the paste-like silver powder composition mentioned above is used, a material weak to heat can also be used as the article 16 to be joined.

  In the bonded body 11 of this embodiment, the substrate 12 and the object to be bonded 16 are bonded by the bonding layer 14. Since the bonding layer 14 is formed using the above-described paste-like silver powder composition, the shear strength of the bonding layer 14 is high. The shear strength of the joined body 11 of the present embodiment is preferably 10 MPa or more, and more preferably 30 MPa or more. The shear strength can be measured using, for example, a commercially available bonding tester (for example, manufactured by RHESCA). Further, the thermal conductivity of the bonding layer 14 is preferably 75 W / mK or more, and more preferably 150 W / mK or more. The thermal conductivity can be calculated from the specific resistance of the bonding layer 14 using the Wiedemann Franz rule.

Next, a method for manufacturing the above-described joined body 11 will be described.
The manufacturing method of the joined body 11 of this embodiment has a lamination process and a sintering process.

(Lamination process)
First, the laminated body which laminated | stacked the board | substrate 12 (1st member) and the to-be-joined object 16 (2nd member) through the above-mentioned paste-form silver powder composition is formed.
Specifically, the first metal layer 13 is formed by laminating metal on the surface of the substrate 12 by a known method. Similarly, the second metal layer 15 is formed on the surface of the workpiece 16. A method for forming a metal on the surfaces of the substrate 12 and the object to be bonded 16 is not particularly limited, and specific examples include a vacuum deposition method, a sputtering method, a plating method, and a printing method.

Next, the paste-like silver powder composition is applied to the surface of the first metal layer 13 by a known method. The method for applying the paste-like silver powder composition to the surface of the first metal layer 13 is not particularly limited. Specifically, for example, a spin coating method, a metal mask method, a spray coating method, a dispenser coating method, a knife Examples thereof include a coating method, a slit coating method, an inkjet coating method, a screen printing method, an offset printing method, and a die coating method.
Next, the object to be joined 16 is placed on the paste-like silver powder composition applied to the surface of the first metal layer 13 so that the second metal layer 15 side is opposed to produce a laminate.

(Sintering process)
Next, the laminated body formed as described above is heated to dry and sinter the pasty silver powder composition, thereby generating the bonding layer 14. The first metal layer 13 and the second metal layer 15 are bonded via the bonding layer 14.

  The heating temperature during the heat treatment is generally 130 ° C. or higher, preferably 150 ° C. or higher. By heating at this temperature, it is possible to form a dense silver film with high heat dissipation and bonding properties. Although there is no restriction | limiting in particular in the upper limit of heating temperature, For example, it can be 250 degrees C or less, Especially 200 degrees C or less.

As heating time in the case of heat processing, 30 minutes or more are preferable, for example. When the heating time is 30 minutes or more, the shear strength of the bonding layer 14 can be increased.
The joined body 11 is manufactured by the above process.

  As described above, since the paste-like silver powder composition is used as a bonding material for generating a bonding layer, the manufacturing method of the bonded body according to the present embodiment has a high heat dissipation and bonding property by heating at a relatively low temperature. Can be manufactured.

<Silver film production method>
Next, the manufacturing method of the silver film of this embodiment is demonstrated.
The silver film obtained by the manufacturing method of this embodiment is used as an electrode of a solar cell element, for example.
The manufacturing method of the silver film of this embodiment has an application | coating process and a sintering process.

(Coating process)
First, the above paste-like silver powder composition is applied to a substrate.
The substrate is selected from the group consisting of silicon, glass, ceramics including a transparent conductive material, a polymer material or a metal substrate, or silicon, glass, ceramics including a transparent conductive material, a polymer material and a metal. It can be a laminate of two or more types. Moreover, it is preferable that a base material is either a solar cell element or a solar cell element with a transparent metal film. As the transparent metal film, indium tin oxide (ITO), antimony-doped tin oxide (ATO), nesa (tin oxide SnO ₂ ), IZO (Indium Zinc Oxide), AZO (aluminum-doped ZnO) ) And the like. It is preferable that the said paste-form silver powder composition is apply | coated to the surface of the photoelectric conversion semiconductor layer of a solar cell element, or the surface of the transparent metal film of a solar cell element with a transparent metal film.

(Sintering process)
Next, the base material coated with the pasty silver powder composition is heated, and the pasty silver powder composition is dried and sintered to form a silver film. The heating temperature is generally 130 ° C. or higher, preferably 150 ° C. or higher. By heating at this temperature, it is possible to form a dense silver film with high heat dissipation. The heating time is generally in the range of 10 minutes to 1 hour, preferably in the range of 15 to 40 minutes. There is no restriction | limiting in particular in a heating atmosphere, It can set arbitrarily in air | atmosphere atmosphere, a vacuum atmosphere, a reducing gas atmosphere, etc. The thickness of the silver film produced by the production method of the present embodiment is generally in the range of 0.1 μm to 2.0 μm, preferably in the range of 0.3 μm to 1.5 μm. If the film thickness becomes too thin, for example, when used as an electrode of a solar cell element, the surface resistance value may be insufficient. On the other hand, if the film thickness becomes too thick, the amount of silver powder used increases and the cost increases.

  According to the method for producing a silver film of the present embodiment, as described above, since the paste-like silver powder composition described above is used as the material for the silver film, a dense silver film can be produced by heating at a relatively low temperature. It becomes.

<Manufacture of silver powder>
(Classification I)
As silver salt aqueous solution, 900 g of silver nitrate aqueous solution (silver nitrate concentration: 66% by mass), as carboxylate aqueous solution, 600 g of aqueous glycolic acid solution (concentration of glycolic acid: 56% by mass), and as a reducing agent aqueous solution, hydrazine aqueous solution (hydrazine concentration). : 58% by mass) of 300 g and 1200 g of ion-exchanged water were prepared. The prepared silver nitrate aqueous solution, glycolic acid aqueous solution and ion-exchanged water were each placed in a glass container and kept at 50 ° C. with a hot water bath. The prepared aqueous hydrazine solution was put in a glass container and kept at 20 ° C. by a water bath.

  First, while stirring ion-exchanged water kept at 50 ° C., a tube pump is used to mix the aqueous solution of silver nitrate kept at 50 ° C. and the aqueous solution of glycolic acid kept at 50 ° C. into the ion-exchanged water. All of the solution was added dropwise over 5 minutes to produce silver glycolate particles to prepare a silver glycolate slurry. The prepared silver glycolate slurry was cooled to 20 ° C. by air cooling.

Next, while stirring the silver glycolate slurry at 20 ° C. with a water bath, the aqueous solution of hydrazine kept at 20 ° C. is dropped into the silver glycolate slurry over 30 minutes using a tube pump while stirring. Thus, a mixed slurry was prepared.
Next, while stirring the prepared mixed slurry, using a rubber heater, the temperature was increased to 92 ° C. at a temperature increase rate of 15 ° C./hour, and maintained at 92 ° C. (maximum temperature) for 0.33 hours. A silver powder slurry was obtained by heat treatment to reduce silver glycolate particles to produce silver particles. The obtained silver powder slurry was cooled to a temperature of 30 ° C. in a water bath for 15 minutes. Next, the silver powder slurry was put in a centrifuge and centrifuged at a rotational speed of 1000 rpm for 10 minutes. The supernatant liquid (liquid layer) was removed, and the remaining solid content (silver powder) was washed with water, and then dried by freeze-drying for 30 hours to recover the silver powder. The recovered silver powder was classified as Class I silver powder.

(Category II)
A silver powder of class II was obtained in the same manner as class I, except that a formic acid aqueous solution (formic acid concentration: 58% by mass) was used as the reducing agent aqueous solution.

(Category III)
Classification was carried out in the same manner as in Class I except that ammonium citrate aqueous solution (citric acid concentration: 56% by mass) was used as the carboxylic acid aqueous solution, and ammonium formate aqueous solution (formic acid concentration: 58% by mass) as the reducing agent aqueous solution. III silver powder was obtained.

(Category IV)
Except for using a malonic acid aqueous solution (malonic acid concentration: 56% by mass) as the carboxylic acid aqueous solution and a sodium ascorbate aqueous solution (concentration of ascorbic acid: 58% by mass) as the reducing agent aqueous solution. A classification IV silver powder was obtained.

(Classification V)
Classification was performed in the same manner as in Class I except that sodium citrate aqueous solution (citric acid concentration: 56% by mass) was used as the carboxylic acid aqueous solution, and ammonium formate aqueous solution (formic acid concentration: 58% by mass) as the reducing agent aqueous solution. V silver powder was obtained.

(Classification VI)
The mixed slurry was heated to 95 ° C. and heated at 95 ° C. (maximum temperature) for 0.5 hours to obtain a silver powder slurry. Obtained.

(Category VII)
A silver powder of class VII was obtained in the same manner as class I except that the mixed slurry was heated at a temperature of 92 ° C. (maximum temperature) for 0.25 hours to obtain a silver powder slurry.

(Classification VIII)
The mixture slurry was heated to a temperature of 70 ° C. and heated at 70 ° C. (maximum temperature) for 0.5 hours to obtain a silver powder slurry. Obtained.

(Classification IX)
The mixed slurry was heated to a temperature of 97 ° C. and heated at 97 ° C. (maximum temperature) for 1 hour to obtain a silver powder slurry. .

<Evaluation of silver powder>
An average particle diameter of the silver powder prepared in classification I~IX, _{C 3 H} 3 _O 3 with respect to Ag ⁺ ions ^- was measured by detecting the amount of the following methods ion ^- ion and _C 6 _H 6 _{O 8.}

(Measurement method of average particle size)
Silver powder was mixed with an epoxy resin, and the resulting mixture was cured to produce a sample for measuring the average particle size. The central part of this sample for measuring average particle diameter was cut, and the cut surface was polished by an argon ion beam. The polished processed surface is observed with an SEM (scanning electron microscope), 1000 or more silver particles are randomly selected, and the diameter of the selected silver particles in the direction along the irradiation direction of the argon ion beam is determined. It measured as a particle diameter and computed the average of the measured particle diameter.

(Ag _C 3 _H 3 against ⁺ ions _{O 3} ^- ions and _C 6 _H 6 _{O 8} ^- method of measuring the detected amount of ions)
The detected amounts of C ₃ H ₃ O ₃ ⁻ ions and C ₆ H ₆ O ₈ ⁻ ions with respect to Ag ⁺ ions were measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS). A sample in which silver powder was buried in the surface of the In foil was used as a measurement sample. The measuring device used was nanoTOFII manufactured by ULVAC PHI. The measurement range was 100 μm square, the primary ion was Bi ₃ ⁺⁺ (30 kV), the measurement time was 5 minutes, and a TOF-SIMS spectrum was obtained. From the obtained TOF-SIMS spectrum, the detected amount of Ag ⁺ ion, C ₃ H ₃ O ₃ ⁻ ion, C ₆ H ₆ O ₈ ⁻ ion was determined, and C ₃ H ₃ O ₃ ⁻ ion and C ₆ H ₆ O were obtained. ₈ ^- a detectable amount of ions, each divided by the detected amount of Ag ⁺ ions, _C 3 _H 3 for Ag ⁺ ions _{O 3} ^- ions and _C 6 _H 6 _{O 8} ^- to calculate the detected amount of ions.

  The results of each measurement are shown in Table 1 below. In Table 1, the types of silver salt, carboxylate and reducing agent used for the production of silver powder and the heat treatment conditions (maximum temperature, holding time) of the mixed slurry are also shown.

<Production of paste-like silver powder composition>
[Invention Example 1]
Silver powder of category I as silver powder, amine polymer dispersant (peak top molecular weight measured by gel filtration chromatography (LC-8020, manufactured by Tosoh Corporation, LC-8020)) as dispersant, and butyl carbitol acetate as solvent Were weighed so that the blending amount would be 87: 3: 10 in parts by mass, and placed in a container. Next, the operation of rotating this container for 5 minutes at a rotational speed of 2000 rpm using a kneader (THINKY, “Awatori Nertaro”) is performed three times to knead the silver powder, the dispersant and the solvent. Thus, a pasty silver powder composition was produced.

[Invention Examples 2 to 11 and Comparative Examples 1 to 9]
A paste-like silver powder composition was produced in the same manner as in Example 1 except that silver powder, a dispersant and a solvent listed in Table 2 were used by weighing in the amounts shown in Table 2. did.

<Evaluation of Pasty Silver Powder Composition>
The applicability of the pasty silver powder compositions produced in Invention Examples 1 to 11 and Comparative Examples 1 to 9 was evaluated. Furthermore, heat dissipation and bondability were evaluated about the silver film (bonding layer) produced using the paste-form silver powder composition. Finally, comprehensive evaluation was performed. The results are shown in Table 3.

(Evaluation of applicability)
The applicability was evaluated from the viscosity of the pasty silver powder composition.
The viscosity of the pasty silver powder composition was measured using a rheometer. The measurement temperature was 25 ° C., a jig having a diameter of 20 mmφ was used, and the viscosity at a shear rate of 10 [/ s] was measured.

  The coating property is ◎ when the viscosity measured by the above method is 15 Pa · s or more and 40 Pa · s or less, and ○ when the viscosity is 10 Pa · s or more and less than 15 Pa · s or more than 40 Pa · s and 50 Pa · s or less. X exceeding 50 Pa · s.

(Evaluation of heat dissipation)
On the glass substrate, the paste-like silver powder composition was applied using a metal mask plate (hole size: length 10 mm × width 10 mm, thickness: 50 μm) to form a coating film. Next, the coating film was heated in an air atmosphere at 200 ° C. for 60 minutes in a muffle furnace to produce a silver film on the glass substrate. And the thermal conductivity of the produced silver film was measured.

The thermal conductivity was calculated using the Wiedemann Franz rule. That is, the sheet resistance value and film thickness of the silver film were measured in an environment at a temperature of 25 ° C. (absolute temperature T = 298K). And specific resistance (sigma) (= sheet resistance value x film thickness) of a silver film was calculated | required, and thermal conductivity K (unit: W / mK) was computed from the following formula.
K = L × T × σ
(L: Lorentz number L = 2.44 × 10 ⁻⁸ WΩK ⁻² , T: temperature = 298 K)

  For the heat dissipation, the thermal conductivity measured by the above method was ◎ for those having a thermal conductivity of 150 W / mK or more, ◯ for those having a thermal conductivity of 75 W / mK or more and less than 150 W / mK, and × for those having a thermal conductivity of less than 75 W / mK. It should be noted that evaluation was not possible if a coating film having a uniform thickness could not be formed on a glass substrate.

(Evaluation of bondability)
An aluminum substrate whose surface is covered with a silver layer and a silicon chip whose surface is covered with a silver layer (bottom surface: 2.5 mm long × 2.5 mm wide, thickness: 200 μm) were prepared. The pasty silver powder composition was applied to the surface (silver layer) of the aluminum substrate using a metal mask plate (hole size: 3 mm length × 3 mm width, thickness: 50 μm) to form a coating layer. Next, the bottom surface of the silicon chip is placed on the coating layer, heated in the atmosphere at a temperature of 200 ° C. for 60 minutes to sinter the coating layer, and a bonding layer is formed between the aluminum substrate and the silicon chip. The obtained joined body was obtained. And the shear strength of the joining layer of the obtained joined body was measured.

  For the shear strength, the force required to break the bonding layer formed between the aluminum substrate and the silicon chip is measured by a bonding tester (manufactured by RHESCA), and this measured value is measured as the bonding area (the area of the bottom surface of the silicon chip). ) To obtain the share strength.

  As for the bondability, the shear strength measured by the above-mentioned method was ◎ when the shear strength was 30 MPa or more, ○ when the shear strength was 10 MPa or more and less than 30 MPa, and × when the shear strength was less than 10 MPa. In addition, the thing which could not form the coating layer with a uniform thickness on the surface of the aluminum substrate was regarded as unacceptable.

(Comprehensive evaluation)
All three evaluation items of applicability, heat dissipation, and heat dissipation were ◎, and one or two of the three evaluation items were ◎, and the rest were ○ The case where all the three evaluation items were “good” was evaluated as “△”, and the case where any one of the three evaluation items was “×” was evaluated as “poor”.

  In Comparative Example 1, heat dissipation and bondability were low. This is because the amount of the organic material covering the surface of the silver particles is excessively increased, so that during the heating of the silver film production, sintering between the silver particles and between the silver particles and the object to be bonded is suppressed. This is probably because the density of the film was lowered. In Comparative Example 2, the applicability was low, and the heat dissipation and bonding properties could not be evaluated. This is considered to be because the adsorption of the polymer dispersant to the surface of the silver particles was caused by the amount of the organic substance covering the surface of the silver particles being too small. The comparative example 3 had low applicability | paintability, and heat dissipation and joining property could not be evaluated. This is considered to be because the effect of suppressing aggregation of silver particles was weakened by using low molecular weight butylamine as a dispersant. In Comparative Example 4, heat dissipation and bondability were low. This is because when the molecular weight of the polymer dispersant becomes too large, it becomes difficult to detach from the surface of the silver particles during heating during the production of the silver film, and sintering between the silver particles and between the silver particles and the object to be joined is difficult. This is considered to be because the density of the silver film was reduced. In Comparative Example 5, it is considered that the effect of the polymer dispersant was not obtained because the content of the polymer dispersant was too small. In Comparative Example 6, heat dissipation and bondability were low. This is because the amount of the polymer dispersant is excessively large, so that the amount of the polymer dispersant remaining on the surface of the silver particles during heating during the production of the silver film increases, This is considered to be because the sintering of the film was suppressed and the density of the silver film was reduced.

  In Comparative Example 7, heat dissipation and bondability were low. This is because the polymer dispersant has a carboxyl group, and this carboxyl group strongly adheres to the silver particles, and the amount of the polymer dispersant remaining on the surface of the silver particles during heating during the production of the silver film is large. Thus, it is considered that the sintering between the silver particles and between the silver particles and the article to be bonded was suppressed, and the density of the silver film was lowered. In Comparative Example 8, the coating property, heat dissipation property, and bonding property were low. The reason why the coating property was lowered is considered to be that the effect of suppressing the aggregation of silver particles became weak because the molecular weight of the polymer dispersant became too small. In addition, the heat dissipation and bonding properties are low because the polymer dispersant has a thio group, and this thio group adheres strongly to the silver particles, and the surface of the silver particles during heating during the preparation of the silver film This is considered to be because the amount of the polymer dispersant remaining on the substrate increases, sintering between the silver particles and between the silver particles and the article to be bonded is suppressed, and the density of the silver film is reduced. Comparative Example 9 had poor applicability. This is considered to be because the dispersion effect was suppressed because the compatibility between the solvent and the polymer dispersant was low.

On the other hand, the paste-like silver powder compositions of Invention Examples 1 to 11 were excellent in coatability, and the silver film obtained by heating at 200 ° C. had high heat dissipation and bondability.
From the above results, according to the examples of the present invention, a paste-like silver powder composition that is excellent in coatability and capable of forming a silver film (silver powder sintered body) with high heat dissipation and high bondability by heating at a relatively low temperature. It was confirmed that it would be possible to provide. In addition, according to the present invention example, a bonded body manufacturing method capable of manufacturing a bonded body having high thermal conductivity and high bonding strength by heating at a relatively low temperature, and high thermal conductivity by heating at a relatively low temperature. It has been confirmed that it is possible to provide a method for producing a silver film capable of producing a silver film.

DESCRIPTION OF SYMBOLS 11 ... Bonded body 12 ... Board | substrate 13 ... 1st metal layer 14 ... Bonding layer 15 ... 2nd metal layer 16 ... To-be-joined object 17, 18 ... Interface

Claims (5)

Silver powder, a polymer dispersant having a nitrogen atom or a phosphorus atom in the molecule, and at least one solvent selected from the group consisting of diols and carbitol acetates,
The silver powder has a detected amount of C ₃ H ₃ O ₃ ⁻ ions and C ₆ H ₆ O ₈ ⁻ ions measured by time-of-flight secondary ion mass spectrometry with respect to the detected amount of Ag ⁺ ions. The detection amount of C ₃ H ₃ O ₃ ⁻ ions is in the range of 0.2 to 1.0 times, and the detection amount of C ₆ H ₆ O ₈ ⁻ ions is in the range of 0.005 to 0.02 times. And
The polymer dispersant has a peak top molecular weight measured by gel filtration chromatography in the range of 1500 to 15000,
The pasty silver powder composition, wherein the content of the polymer dispersant is in the range of 1% by mass to 5% by mass.   The pasty silver powder composition according to claim 1, wherein the polymer dispersant is a polymer dispersant having an amino group or a phosphate group.   The pasty silver powder composition according to claim 1 or 2, wherein the solvent is ethylene glycol, 2-ethyl-1,3-hexanediol, or butyl carbitol acetate. A method for manufacturing a joined body in which a first member and a second member are joined via a joining layer,
The lamination process which forms the laminated body which laminated | stacked the said 1st member and the said 2nd member through the paste-form silver powder composition of any one of Claim 1 to 3,
A sintering process in which the laminate is heated to dry and sinter the paste-like silver powder composition to form a bonding layer;
A method for producing a joined body, comprising: An application step of applying a paste-like silver powder composition according to any one of claims 1 to 3 to a substrate;
Heating the substrate coated with the paste-like silver powder composition, drying and sintering the paste-like silver powder composition to produce a silver film; and
A method for producing a silver film, comprising: